This invention pertains to disk storage devices and more particularly to rigid magnetic disks for use in such devices.
In rigid magnetic disk drives, glide heads are used to identify disks with mechanical projections high enough above the surface to contact the data head during normal file operation. Currently available products are concerned when projections or asperities have a height of 5 microinches or greater. To identify asperity causes and take corrective action it is necessary to locate these sites on the disk surface. A tester using glide heads can accurately give the angular and radial position of the glide head when an asperity contacts the head. The uncertainty of the asperity location relative to these coordinates is caused by the rail area on the glide head, the accuracy of the actual coordinates and the relocating tolerances in taking the disk from the glide tester to a microscope viewing station. When the area of the asperity becomes very small (about 4 micrometers in diameter), it becomes nearly impossible to repeatedly locate the defect in this relatively large uncertainty zone.
Although this problem is difficult at present, it will become more severe in the future as the bit and track densities on magnetic disks are increased. Such increased densities will require thinner magnetic coatings and lower transducer head flyheights which will require that the maximum tolerable asperity be less. Accordingly, the projections which require identification will be smaller.